Electron tube



y L@ @ci if March -2, 1937.

F. SCHRTER ET A1. ELECTR'N TUBE Filed Aug. 8, 1932 @Emst-@- INVENT fm2 5mm mrz BY r rarenreci Mer. z, w61

ELECTRON TUBE Fritz Schrter and Fritz Miclielssen, Berlin, Ger- Iilany, assignors to Telefunken Gesellschaft fur Drahtlose Telegraphie m. b. II., Berlin, Germany, corporation of Germany E Application August 8, 1932, Serial No. 627,926 In Germany August 29, 1931 2 Claims. (C1. Z50-27.5)

The present `invention relates to electron tubes of the cathode ray type and particularly to ways and means by which the electron pencil may be concentrated at the` point on the fluorescent found satisfactory to carry out the aims and objects above set forth, and by Figs. 2 and 3 suitable modiiications of the arrangement of Fig. 1. Referring now to the embodiment of the inven- 5 screen at which it impjnges, y tion shown by way of example in Fig. 1, the letter 5 It is known that for the production of a sharply K represents the directly indirectly heated clecpencilled or focused electron ray bundle such as trode (the possible heating means including also required, for instance, in Braun tubes, a rather glow-discharge or equivalent means),from which large number of auxiliary means and ways have electrodes the electrons enter into the free space.

lbeen suggested in the prior art. One of these Ai designates an electrode provided with a dia- 10 schemes consists of the disposition of a so-called phragrn aperture, this electrode being maintained Wehnelt cylinder about the electron emitting at a positive potential in reference to the cathode body of the cathode, The Wehnelt cylinder serves K. The cylindrical electrode Z by the potential the object, by virtue of its potential, of'focusingof which the electrons issuing from electrode A1 the emission of the cathode upon a diaphragm in a diiuse manner are concentrated upon the 15 portion of the accelerating anode. The concenanode diaphragm proper, as indicated at A2, such tration of the pencil issuing through the anode focusing or concentrating action being optiondiaphragm, if desired, may be further promoted ally promoted by the constrictive effect of a gas by the constrictive action of a low pressure gas filling is arranged to surround substantially the l0 atmosphere. electrode A1. Instead of the cylindrical forma- 20 However, in the course of research work with tion of the concentrating electrode Z, also other the above and similar arrangements, it has been forms may Abe chosen which, for instance, may discovered that a prerequisite for permanent satbe in the shape of a planar electrode having a isfactory focusing is to provide a fixed or sharply diaphragm.

bounded source of electrons which results in the The scheme of modulating the intensity of the 25 radiation or pencil. For instance, if the cathode cathode ray pencil by the potentials of such a member of the arrangements used in the prior Wehnelt cylinder as is known in the earlier art art, after some prolonged period of operation, no in th-e present instance may be used in such a a longer gives uniform emission, this becomes caus- Way that it S blOllgllt t0 aCL UDOD the .my DSDC ative of a shift in the origin of the pencil, which issuing from the SECOUdaIY eleCtlOde (CathOd) 30 in turn means that the effect of the anode and In some cases the concentrator electrode Z may cylinder potentials is no longer focusing so far be entirely dispensed with by pencilling or focusas the new origin or source of the electrons is ing the electron ray pencil merely by the con-l concerned. While it is occasionally feasible to striotive action of slight gas traces.

adjust the same to the values required for o, What is essential for the invention is that the 35 sharply focused pencil, it will in the majority of arrangements are so chosen that a secondary cases be found that subsequent improvement of cathode designated at A1 iS used to act 21S the conditions is not possible. source or starting point of the electron ray pen- The present invention therefore has as its pricil rather than the emissive cathode K proper.

40 mary object that of disclosing ways and means In such a scheme the dimensions of the primary 40 adapted to overcome the difficulties of the prior cathode K and of the secondary cathode A1 are art and thus to insure a sharply focused cathode suitably so chosen that the diaphragm aperture ray pencil in a reliable manner for long periods of Ai is situated at close proximity to the cathode of time. The invention also provides means K, While the other parts of electrode A1 are at whereby the intensity of the emitted electron a greater distance from the heated cathode than 45 pencil may be iniiucnced in the desired manner the edge constituting the diaphragm, in a way as and to modulate the same in a manner such as roughly shown by Fig. 2. The result isthat nearto insure reliable operation wherever this is dc ly the entire emission current issuing from cathsirable, as, e. g., in television work. According to ode K, owing to the accelerative effect of the pothe present invention these results are accom-l tential of electrode Ai across the diaphragm in 50 plished by shifting the origin of the pencil to be A1 enters into the free space where it is subjected used in connection with the purposes of the tube to the concentrating action of the other factors, to a secondary cathode disposed in the vicinity e. g., the potentials of the concentrator electrode of the electron-emissive element instead of using Z and anode A2 as well as the constiictive action the electron ray pencil from the electron emissive produced by gas ions. 55 cathode, the latter being either of the directly or In choosing the values of the potentials of elecindirectly heated type. trodes Z and A2 and the through action of the The accompanying drawing serves to illustrate plate potential of electrode A2 upon the origin of the principles of the invention and discloses by the ray pencil, as will be understood, these will 00 Fig. l a form of the invention which has been be different from what they are in the case of 60 be seen that the anode potential and the cylinder potential will be called upon to produce a concentrative action upon substantially faster electrons than is true in the case of arrangements used in the prior art. However, as a new merit of this arrangement it is discovered that even after operation during long periods, when the electrons of the heated cathode K are emitted from another Apoint than initially the origin of the cathode ray pencil on the diaphragm A1 will be unaltered.

The invention offers further advantages as regards the modulability of the pencil intensity. According to the invention, as before pointed out. it is feasible to control and regulate the intensity of the secondary ray pencil, for instance, by the alternating current potentials of the concentrating electrode (Wehnelt cylinder or other form of electrode) or else by -direct current magnetic fields. However, in some instances, this embodiment involves demerits. Since according to the invention the pencil originates from the secvondary cathode it will be' seen that it is possible to dispense with the co-action of such concentrator or focusing elements as the Wehnelt cylinder in the modulation of the pencil. The emission of the secondary electrode is not subject to the thermal inertia of emissive cathodes. By appropriate circuit means it is possible to modulate the Very emission of the secondary cathode at the rhythm or rate of the frequencies to be impressed upon the ray pencil. The simplest scheme of this kind is shown by way of example in Fig. 1, where the alternating current potentials are impressed upon the electrode A1 acting as the secondary cathode, for the purpose of regulating the electron emission issuing from the diaphragm, whereas the concentrating electrodes Z and A2 carry only direct current potentials. It will be understood that it is also feasible ac cording to this invention to apply only alternating current potentials to the secondary cathode, or to apply the modulating potential in series with a direct current potential.

Occasionally this troublesome action may arise in an arrangement as just described, namely, that, while the emission of the secondary cathode may be regulated by the. alternating current potential of A1, also the velocity ol the electrons at the origin of the ray pencil may fluctuate at the rhythm of the modulator frequency inasmuch as this alternating current potential exercises an accelerative action upon the electrons issuing from the secondary cathode diaphragm. In many cases these slight nuctuations of energy of vthe electrons will not occasion any troublesome effects. But if, for instance, the cathode ray pencil is to be. operated only with very low potentials at A2 (say, 100 v.), the energy content (volume) of the electrons varying at the rhythm of the secondary cathode potential may make itself felt, e. g., by a decrease in sharpness of the ray pencil.

Also, these difficulties can be overcome according to this invention by regulating the emission of the secondary cathode by electric or magnetic circuit means, and then it will be the volume of the electrons issuing from the diaphragm Ai rather than the velocity thereof that is controlled, whereas the electrode acting as the real secondary cathode is operated only with a constant dlreet current potential.

An embodiment of this sort is illustrated by way of example in Fig. 3. In this scheme a grid G is interposed between the indirectly heated primary cathode K and the electrode A1 acting as a secondary cathode and having a positive potential, the potentials of the said grid G being capable of controlling the volume of the electrons flowing to A1 and across the diaphragm of Ai. The concentrating electrode is supposed to consist of a flat diaphragm electrode W. By choosing suitable dimensions for the grid G, the secondary cathode emission may be shifted in the range of negative grid'potentials so that gridi current need not necessarily become a source of trouble, if in addition to the alternating current potential the right bias is imparted to the grid. It is to be noted that there are also other practicable ways and means with a view to inluencethe emissionof Ithesecondarycathodeetl,

for instance, by means of magnetic fields or by the control action of plate potentials as used, for example, in connection with the plation.

As regards the utilization of such cathode ray pencils originating at a secondary cathode there exist the same chances as in the embodiments' heretofore known in the art. After having passed through the anode diaphragm A2, they may be deflected in any desired direction, for instance, by means of electric delector plat-es or by magnetic elements, and may be employ-ed as a safe and dependable operating element in a Braun tube for widely varying purposes in connection with measuring or television work. l

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

1. An electron tube comprising an envelop-e containing at one end a fluorescent screen and at the opposite end an electron emitting cathode, a secondary cathode substantially surrounding the electron emitting cathode and adapted to produce an effective concentrated electron source, a concentrator electrode adapted to produce jointly with the secondary cathode a conical electrostatic field adapted to focus the electron beam at a predetermined point, a control grid interposed between the primary cathode and the secondary cathode to control in accordance with the potential thereof the concentration and dispersion of the generated electron beam, and an accelerator electrode to control the velocity of impact of the concentrated electron beam upon the electron tube fluorescent screen structure.

2. A cathode ray tube comprising a source of cathode rays, a secondary cathode adapted to produce the effect of a concentrated electron source, said secondary cathode substantially surrounding the primary cathode, a tubular concentrator electrode extending beyond the secondary cathode in the path of the electron stream issuing therefrom and adapted to produce jointly with the secondary cathode a conical electrostatic eld serving to focus the generated electron pencil to a sharply dened point at a predetermined distance from the source, and an accelerator electrode interposed between the concentrator electrode and the focus point for controlling the velocity of the cathode ray pencil within the envelope.

FRITZ SCHRTER. FRITZ MICHELSSEN. 

